U.S. crude-oil output is soaring, but a number of factors point to a decline in oil prices, ranging from refinery shutdowns to futures strategies.

Here's a puzzle: The U.S. is producing the most crude oil in decades, domestic stockpiles are at record highs, yet oil prices are near $100 barrel. What's keeping prices aloft?

The first piece of the puzzle is the way the U.S. prices its oil. The U.S. benchmark, known as West Texas Intermediate, or WTI, is based on delivery at a storage hub in Cushing, Okla. How much oil is stored in Cushing affects...